1. Field of the Invention
The present invention relates to a method for forming a plug and more particularly, to a method for forming a conductive plug in a contact hole without a cavity formed therein.
2. Discussion of the Related Art
When a high integrated device is manufactured, due to low step coverage of a metal layer such as titanium(Ti), titanium nitride (TiN), titanium tungsten (TiW), or aluminum, the process of metal wiring is facilitated after the deposition of a tungsten layer. That is, the tungsten layer is deposited in a metal contact hole or a via and etched-back to form a tungsten plug. However, since tungsten is grown on an oxide layer at a low speed, a glue layer made of Ti, TiN, or TiW is required prior to forming the tungsten layer to ensure the formation of the tungsten layer. In this case, the above process can proceed without removing the glue layer after the tungsten layer is etched-back. On the other hand, the above process may proceed after removing the glue layer in order to minimize loss of the tungsten plug for a stacked structure having more than 4 wires, such as a logic device.
A conventional method for forming a conductive plug in a contact hole will be discussed with reference to the attached drawings.
As shown in FIG. 1a, on the entire surface of a substrate 1, there is formed an interlayer insulating layer 2 using a chemical vapor deposition (CVD) process or a thermal oxidation process. A photoresist layer is coated on the surface of the interlayer insulating layer 2 and then exposed and developed to form a patterned photoresist layer. With the patterned photoresist layer serving as a mask, the interlayer insulating layer 2 is anisotropically etched to form a contact hole 5 on a predetermined portion of the substrate 1. Subsequently, on the resultant surface, there is formed a glue layer 3, which is a barrier layer, made of titanium (Ti), titanium nitride (TiN), or titanium tungsten (TiW) on the interlayer insulating layer 2 and in the contact hole 5. Thereafter, a tungsten layer 4 is formed over the substrate 1 using a CVD process.
Referring to FIG. 1b, the tungsten layer 4 is etched-back using fluorine gas that is injected into a plasma reactor, thereby the fluorine gas etches the tungsten layer 4 to form a tungsten plug 4a in the contact hole 5.
Referring to FIG. 1c, the glue layer 3 is etched using chlorine (C1.sub.2) gas, argon (Ar) gas, helium (He) gas, or oxygen (O.sub.2) gas in the plasma reactor. In this case, due to the chemical etching properties between chlorine gas and the glue layer 3, the glue layer 3 on the interlayer insulating layer 2 is etched away as well as a portion of the glue layer 3 in contact with a side of the interlayer insulating layer 2 in the contact hole. As a result, a serious plug cavity 6 is formed.
A conventional method for forming a conductive plug in a contact hole has the following problems.
First, a portion of the glue layer that is in contact with an interlayer insulating layer is over-etched, which forms a plug cavity.
Second, due to the plug cavity, a void is generated in a metal wiring process that decreases the reliability of a unit device.